This invention relates to quantum non-locality modulated signaling methods.
It has been demonstrated, by Aspect and others, that under some circumstances, certain atomic species and non-linear down conversion crystals can be induced to emit entangled pairs of photons that have correlated linear polarizations; the correlated linear polarizations of the photon pairs will be found to be either always mutually orthogonal, or mutually parallel, depending on the nature of the source, when observed in any linear polarization basis. The photons can be provided in separate streams, with either one of each pair in each stream or with each photon having an equal probability of being found in either stream. It has further been strongly demonstrated that, under certain conditions, these entangled photons are not emitted with any predetermined directions of linear polarization, but that the linear polarization states of both photons only become definite upon measurement of the linear polarization of one of the photons. Thus, assuming perpendicular polarization correlation, if one photon is measured to be vertically polarized, then the other photon becomes horizontally polarized at that moment, no matter how far apart the two photons have traveled prior to the measurement. The polarization states of the two photons are 100 percent entangled; measurement of the horizontal or vertical polarization state of one photon determines the vertical or horizontal polarization state, respectively of the other (where the linear polarization correlation of the entangled photons is perpendicular), but prior to measurement, their polarization states are indefinite. In essence, the two photons are parts of the same quantum object; regardless of how far the photons travel apart from each other, changing the properties of one photon instantly changes the properties of the whole object, including the properties of the other photon. The experiments of Aspect, et al., have convinced most quantum theorists that the polarizations of these entangled photons are non-local; the polarizations are not predetermined at the time of emission, but are rather condensed into a particular state at the moment of xe2x80x9cobservationxe2x80x9d of one of them. A. Aspect, P. Grangier and G. Roger, Phys. Lett. 47, 460 (1981) and 49, 91 (1982). A. Aspect, J. Dalibard and G. Roger, Phys. Lett. 49, 1804 (1982); Z. Y. Ou and L. Mandel, Phys. Lett. 61, 50 (1988) and 61, 54 (1988).
The correlation of properties between space-like separated entangled quantum objects has been called the EPR effect, after the scientists Einstein, Podelsky, and Rosen, who first proposed that quantum mechanics predicted that the measurable properties of such entangled quantum objects could be non-local. Various recent experiments have demonstrated that the EPR effect occurs faster than the speed of light; the speed of the EPR effect is presumed to be instantaneous.
Various quantum theorists and experimentalists have addressed the question of whether the non-locality effects of entangled particles can be employed as the basis for sending information. The published conclusions of Aspect and others have asserted that such is not possible. Baggott, Jim, The Meaning of Quantum Theory, Oxford Science Publications, Oxford University Press, 1992, pp. 148-150; P. Eberhard and R. Ross, Found. Phys. Lett., 2, 127 (1989). Their logic is that the passage rate of either stream of entangled photons through its respective polarizer will always appear random. Although the correlation of polarization between the two photons is not random, the probability distribution of both the sender""s and the receiver""s photons will be uniformly distributed into the two observed polarization states, so the receiver cannot glean information from the photons he, alone, receives. The signal and the noise are, therefore, of equal magnitude.
These conclusions are correct, so far as they go. In the systems which have been previously analyzed, the entangled photon source, emitting photons in a xe2x80x98singletxe2x80x99 state, the quantum state superposition of horizontal and vertical polarization with equal probability amplitudes, is placed midway between the sender and the receiver, two linear polarizers are employed, one at each end of the dual photon stream, one polarizer for the sender and one for the receiver, and the photon coincidence count rate for photons passing through the two polarizers is measured as a function of the angles of the polarizers. It does appear to be true that information cannot be sent by correlation of entangled photon polarizations by means of such an apparatus designed especially for coincidence counting. Indeed, coincidence counting itself implies the existence of a classical (non-quantum) channel over which to identify coincident detector events.
It appears that prior researchers in this field have assumed that information cannot be transmitted by polarization correlation using an apparatus consisting of an entangled photon source in the singlet state, two polarizers, and two or more detectors, and that it is therefore impossible to transmit information via quantum correlations between space-like separated photons in general. It has also been commonly assumed that once a photon passes through a linear polarizer its polarization state is fixed, and that passage of polarization-entangled photons through polarizing elements causes loss of polarization entanglement. Yet another key assumption by physicists is that the entanglement of a pair of quantum objects can only persist so long as the entangled pair exists in a superposition of joint quantum states.
The commonly held belief that information cannot be transmitted via quantum correlations between space-like separated entangled photons is based on the above assumptions. I have discovered that these assumptions are incorrect. In particular: a polarization-entangled photon pair does not become disentangled if one or both of the photons pass through a polarizer; existing in a superposition of joint quantum states is not a requirement for the persistence of entanglement in polarization entangled photons; and the polarization state of a photon is not immutably fixed by interaction with a polarizer. This correct understanding of the quantum physics of polarization-entangled photons, quantum entanglement, and photon polarization makes clear the utility of my invention.
By means of a quantum mechanical wave function analysis of a polarization-entangled photon experiment performed by T. Haji-Hassan, et. Al., I have discovered that the passage of one or more photons of an entangled photon pair through a polarizing element does not cause loss of polarization entanglement and that existing in a superposition of joint quantum states is not a requirement for the persistence of entanglement. Steenblik, Richard A., Experimental Proof that Passage Through a Polarizer Does Not Cause Loss of Entanglement, Dec. 10, 1998, attached hereto as Appendix A. T. Haji-Hassan, A. Duncan, W. Perrie, and H. Kleinpoppen, xe2x80x9cPolarization Correlation Analysis of the Radiation from a Two-Photon Deuterium Source Using Three Polarizers: A Test of Quantum Mechanics versus Local Realismxe2x80x9d, Phys. Rev. Lett., 62, 237 (1989).
By means of the xe2x80x98Three-Polarizer Experimentxe2x80x99, described in the following pages, it is easily demonstrated that a definite polarization state of a photon in one polarization basis may be altered by subsequent polarization operations on that photon. The polarization state of a photon is therefore not xe2x80x98fixedxe2x80x99, or immutable, until it has actually been detected by absorption.
Based on these correct understandings of polarization-entangled photons, quantum entanglement, and photon polarization, I have discovered that additional polarizers, when properly arranged and controlled, allow the separation of signal information from noise in a singlet state entangled photon system and enable the use of such a system for the transmission of information. Furthermore, I have discovered that it is possible to employ quantum correlation effects to transmit information utilizing only two polarizers if the entangled photon source emits photons in a definite polarization state instead of in the singlet state. These ends are achieved without the need to perform correlation measurements.
Unlike previous entangled quantum particle communication methods, the subject invention does not require that both photons of an entangled pair be sent to the receiver so that coincidence counts may be performed. In fact, if polarization correlation measurements or coincidence count measurements are performed, the correlations may appear to be random. Furthermore, signaling is not accomplished by means of a xe2x80x98one photon per bitxe2x80x99 control means, but by using the control means to alter the probability distribution of a plurality of photons. There is no control over the observed polarization state of any particular entangled photon pair; the control is over the probability distribution of the superposition of polarization states of a plurality of entangled photon pairs. This control of the probability distribution of the entangled photon pairs is accomplished by means of a modification of the state of one or more elements of the apparatus. In essence, it is not the final observed state of isolated entangled photon pairs which carries information, but rather the probability distribution of a plurality of entangled photon pairs which carry information. The control of the probability distribution of the entangled photon pairs is accomplished via control of the state of the apparatus, so it is ultimately the state of the total apparatus which is communicated.
It is a well known principle in quantum mechanics that the probability distribution of the observed states of quantum objects depends both on the quantum objects"" superposition of states and the state of the measurement apparatus, including the choice of quantum property which is observed. The apparatus of my invention is considered to include; an entangled photon source, the system at the sending end, the system at the receiving end, and the entangled photon streams which connect these. A change in the apparatus at the sending end immediately and nonlocally affects the observations at the receiving end since the two ends of the apparatus are connected by single quantum objects which have a physical presence in both space-like separated locations.
It is, therefore, an object of the invention to provide a means and apparatus for sending information by control of non-local correlation effects in entangled pairs of quantum objects.
It is a further object of the invention to provide a means and apparatus for sending information with a transmission speed which is faster than the speed of light in a vacuum by control of non-local correlation effects in entangled pairs of quantum objects.
It is an additional object of the invention to provide a means and apparatus for linking two physically separated measurement apparatus by means of quantum non-locality effects.
It is yet another object of the invention to provide a means and apparatus to establish a co-temporal reference point for two space-like separated timekeeping apparatus via faster than light, substantially instantaneous, signaling.
It is yet another object of the invention to provide a means and apparatus for communication between two space-like separated points which is resistant to eavesdropping by a third party.
It is a further object of the invention to provide a means and apparatus for multiplexed signaling by control of non-local correlation effects in non-degenerate entangled photon pairs.
It is yet an additional object of the invention to provide a means and apparatus for signal transmission between the constituent elements of a computing device, computing system, or computing network.
It is an additional object of the invention to provide a means for sending information by the transmission of one quantum object of a pair of quantum objects to a receiver, the transmission of the other quantum object of a pair of quantum objects to a sender, and to control the quantum state probability distributions of the receiver directed quantum object by means of control of the quantum state probability distributions of the sender directed quantum object.
The subject invention is based on two quantum physics effects: the non-local correlation of quantum states of paired quantum objects and the interaction of individual quanta with a certain sequential arrangements of spin selection devices.
Quantum mechanics is a very successful set of rules and mathematical operators which can be used to predict the statistical behavior of a large number of quantum objects such as fermions, atoms, and bosons, and including, in particular, photons, the quantum units of light. Quantum mechanics does not explain why these rules work, nor why they exist in the first place. The meaning of the rules and their underlying philosophy is open to wide interpretation. The most widely accepted interpretation of quantum mechanics is called the Copenhagen Interpretation. One of the main tenets of the Copenhagen Interpretation is that the specific properties of a quantum object are indefinite until the moment of observation or detection of that object. Science, Vol. 270, DEC.10, 95, pp. 1439-1440. The experiments of Aspect and other researchers strongly support that this is true, especially for photons. Aspect 3 papers, Ou and Mandell, Baggott, supra.
Because of this principle, when quantum objects interact with each other, their quantum states are entangled and the subsequently measured properties of the objects are linked, or correlated. Since the original interaction involves the conservation of energy, momentum, quantum number, or other property, the joint quantum states of the entangled quantum objects must satisfy the appropriate conservation laws when they finally are measured. Furthermore, since the properties of each quantum object are indefinite until the moment of measurement, the only way that the conservation laws can be satisfied is if the act of measurement of the quantum state of one of the entangled quantum objects causes its entangled-pair quantum object to attain the quantum state required to satisfy the conservation laws. The Copenhagen Interpretation proposes that the act of measurement of one quantum object of and entangled pair of quantum objects xe2x80x9ccollapsesxe2x80x9d the quantum state superposition of the of the other quantum object to the required quantum eigenstate.
In the case of entangled photons, the linear polarizations of a pair are 100 percent entangled, either polarized mutually parallel or mutually polarized orthogonal, or perpendicular, to each other (Type I and Type II, respectively) according to the manner of their creation and subsequent optical manipulations, in order for the law of the conservation of angular momentum to be satisfied. These polarization correlation states, parallel correlation and perpendicular correlation, are observed to hold for any consistent polarization measurement orientation.
All attempts to visualize quantum objects fall short of reality, but the following analogy may be of use. Imagine that the photons of a parallel correlation entangled pair represent the two ends of a constantly lengthening, perfectly rigid rod, and further imagine that both ends of this rod look like the blade of a standard screwdriver, with the direction of the blade representing the linear polarization direction of the photon associated with it. Upon emission the photons are in a superposition of quantum states, such as horizontal and vertical, so each end of our imaginary rod would appear to be shaped like an X, with two xe2x80x98half-realxe2x80x99 screwdriver blades at 90 degrees to each other. Only one polarization direction can materialize for each photon at the time of observation, so the parallel-oriented blades at opposite ends of our rod are correlated to each other; either the horizontally oriented blades will materialize or the vertically orientated blades will materialize, but one horizontal blade at one end and one vertical blade at the other end will not materialize. When one photon passes through a polarizer and is detected it is forced to attain one of the definite linear polarization states of its superposition of states, while the perpendicular state potential ceases to exist. Upon observation of the polarization state of one photon we can therefore imagine the corresponding screwdriver blade direction materializing, and the perpendicular blade direction disappearing, at both ends of the rod. Thus the observation of the polarization state of one photon collapses the superposition of polarization states of both photons, forcing the remaining photon at the opposite end of the rod into a definite polarization state parallel to that of the first.
The second effect employed in this invention involves the specific nature of the interaction of quantum objects with spin selection devices. For example, the interaction of light with polarizers is usually explained in terms of electromagnetic wave theory, in which a polarizer selectively absorbs (or reflects) the vector component of the electric field which is perpendicular to its polarization axis. This view is a satisfactory rule of thumb to use when dealing with huge numbers of photons, but the behavior of individual photons must be understood in terms of quantum physics.
Polarization is the term used to identify the quantum property of spin for photons, so polarizing devices can therefore be considered to be spin selection devices for photons. A linear polarization basis is the polarizer orientation defined by the pair of orthogonal linear polarization states which are separated by a polarizer. Linear polarizers separate photons into one of two orthogonal polarization directions, such as 0xc2x0 and 90xc2x0 (commonly called the horizontal/vertical, or {H,V}, basis), +45 degrees and xe2x88x9245 degrees (the {+45,xe2x88x9245} basis), or at any arbitrary angle xcex8xc2x0 and its orthogonal angle (xcex8+90)xc2x0(a{xcex8,xcex8+90}basis). Polarization bases which are at 45xc2x0 to each other are called complimentary, so the {H,V} basis and the {+45,xe2x88x9245} basis are complimentary bases. According to Heisenberg""s Uncertainty Principle, a photon which has a definite polarization state in one basis, such as V in the {H,V} basis, exists in a completely indefinite polarization state in a complimentary basis, such as the {+45,xe2x88x9245} basis. A photon never has a definite polarization state in all linear polarization bases. It can only attain a definite linear polarization state in one polarization basis at any one time.
When randomly polarized, or unpolarized, light impinges upon a linear polarizer, approximately 50 percent of the light is passed and 50 percent is absorbed or reflected, depending on the type of polarizer and its efficiency. Prior to impinging on the polarizer, the photons exist in a superposition of polarization states that provide equal probability amplitudes for the photons to attain any linear polarization state. Half the photons impinging on the polarizer attain the polarization state which passes through the polarizer, while the other half of the photons attain the polarization state which is absorbed by the polarizer. The statistics of large numbers of photons show that half pass and half are absorbed, but each individual photon is either passed or absorbed; an individual photon is never partially absorbed and partially passed. The photons behave in a binary manner, attaining one polarization state or the other. This leaves those photons which pass through the polarizer in a definite polarization state in the basis of the polarizer.
It is commonly known that if a second polarizer is placed in the path of the light after it passes through the first polarizer, the percent of light passing this second polarizer depends on the angle of its polarization axis with respect to the first polarizer. If the polarization axes are parallel, virtually all of the light passing the first polarizer will also pass the second. If the polarization axes are orthogonal to each other, i.e., crossed, or at 90 degrees to each other, almost all of the light passing the first polarizer will be blocked, or absorbed, by the second polarizer. The small amount of light which does get through is called leakage, and it is a measure of the efficiency of the polarizers. High efficiency polarizers have a very low leakage level when crossed, on the order of {fraction (1/10)}th of one percent (e.g., Glan-Thompson polarizing prism Newport part number 10GT04AR.14). It is probably impossible to provide perfectly efficient polarizers because of photon tunneling effects.
Referring to a pair of crossed polarizers, their important feature is their orthogonal polarization axes. For simplicity, let us assume that the polarizers are perfectly efficient and that the first polarizer passes horizontally polarized photons and that the second polarizer passes vertically polarized photons. We will assume that prior to encountering the first polarizer the polarization state of each photon is indefinite, as is the case for thermal sources, such as a candle flame. Upon encountering the first polarizer, a photon must attain either a vertical polarization state or a horizontal polarization state. The photon has an equal probability of attaining either state. If a vertical polarization is attained, the photon will be absorbed; its polarization has now been observed. If it attains a horizontal polarization, it will be passed by the polarizer. It is important to note that while a photon which passes through a polarizer exists in a definite polarization state in the basis of that polarizer, its polarization state is completely indefinite in a complimentary polarization basis.
It is known that undisturbed photons which pass through a horizontal polarizer will not subsequently pass through a vertical polarizer. When a horizontally polarized photon encounters the second, vertical, polarizer it is absorbed. The probability of attaining a vertical polarization state, and passing through a vertical polarizer, is zero for a photon which is in a definite horizontal polarization state.
Now the third polarizer enters the experiment. The first polarizer encountered by a photon is usually called the polarizer, and the second is called the analyzer. The third polarizer is placed in between the polarizer and the analyzer, and it will be called the gate. Let us assume that in this three polarizer experiment the gate is oriented with its polarization axis parallel to the polarizer. In this orientation the gate will have no effect on the passage of photons through the analyzer; the photons which pass through the polarizer will also pass the gate and be stopped by the analyzer. If the gate is oriented parallel to the analyzer, it will also have no effect on the passage of photons through the analyzer because the gate then acts like the analyzer and the photons which pass the polarizer are stopped by the gate, so they never even get to the analyzer.
A peculiar thing happens when the gate is oriented at an angle which is not parallel to either of the other polarizers. It is convenient to choose the angle of the gate to be 45 degrees from both the analyzer and the polarizer. Recall that a photon passing through the first polarizer has a definite horizontal polarization but the polarization state of this photon is completely indefinite in the {+45,xe2x88x9245} linear polarization basis of the gate. When this photon encounters the gate it must attain a new polarization state consistent with the basis of the gate. It must attain a polarization state parallel to the polarization axis of the gate or perpendicular to it, and be passed or absorbed, respectively. The photon has an equal probability of attaining either of these states, but it upon encountering the gate it cannot exist in a superposition of both states.
If the photon passes the gate, it has attained definite polarization state of 45xc2x0 degrees in {+45,xe2x88x9245} polarization basis, but it now has an indefinite polarization state in the original {H,V} basis. Since the photon now exists in a superposition of states in the {H,V} basis it has an equal probability of attaining either the H polarization state or the V polarization state if subsequently forced to do so. Upon encountering the analyzer the photon either attains an H polarization state and is absorbed by the analyzer, or it attains a V polarization state and is passed through the analyzer. Half of the photons which survive passage through both the polarizer and the gate will pass the analyzer with a V polarization state.
Thus, some of the photons which passed through the first polarizer, having attained a definite H polarization, are allowed to attain a definite V polarization and pass through the analyzer because they were forced to attain a definite polarization state in a complimentary polarization basis in between the polarizer and the analyzer. This is commonly referred to as a quantum eraser operation, in which a photon""s definite polarization state in one basis becomes indefinite in that basis by subsequently forcing the photon to attain a definite polarization state in a complimentary basis.
The proportion of photons which pass each of the polarizing elements is 50 percent, so the probability or proportion of photons which make it all the way through all three polarizing elements is (0.5xc3x970.5xc3x970.5)=0.125, or 12.5 percent. These are the photons that make all of the xe2x80x9crightxe2x80x9d decisions at each polarizer. The remainder, 87.5 percent, make one xe2x80x9cwrongxe2x80x9d decision somewhere along the way and get absorbed.
Put in terms of the Dirac notation of the quantum mechanics wave function formalism, the three polarizer experiment can be analyzed as follows: A photon in an initially unpolarized state can be represented as having a superposition of linear polarization states in a chosen basis, such as the {H,V} basis:
|xcexa8 greater than =1/2(|H greater than +|V greater than ).
After passing through a polarizer oriented in the {H,V} basis the photon attains a definite polarization state, such as
|xcexa8 greater than =|H greater than .
This definite linear polarization state in one polarization can be xe2x80x98erasedxe2x80x99 by causing the photon to attain a definite polarization state in a complimentary basis, such as
|xcexa8 greater than =|xe2x88x9245 greater than ,
in the {+45,xe2x88x9245}basis. T. Herzog, P. Kwiat, H. Weinfurter, and A. Zeilinger, xe2x80x9cComplimentarity and the Quantum Eraserxe2x80x9d, Phys. Rev. Lett., 75, 3034 (1995). This leaves the photon in a superposition of states in the original polarization basis
|xcexa8 greater than =1/2(|H greater than +|V greater than ).
Passage of the photon through a polarizing element aligned with the original polarization basis (the {H,V} basis) may then result in the photon attaining a definite polarization state which is orthogonal to the original definite polarization state, such as
|xcexa8 greater than =|V greater than 
in this example. It is thus demonstrated that the definite polarization state of a photon in one polarization basis may be altered by subsequent polarization operations on that photon, and the probability distribution of its polarization states can be thereby controlled. It is clear that the polarization state of a photon only becomes determinate, or fixed, at the time of xe2x80x98observationxe2x80x99, or xe2x80x98measurementxe2x80x99, which is the moment of the absorption of the photon by an electron. At that moment the photon ceases to exist and its properties are not subject to further change.
I have performed three-polarizer experiments with lasers, which, by virtue of their large photon flux and large temporal coherence length, approximate the classical physics limit of continuous transverse electromagnetic waves, with results as described above. I have also performed three-polarizer experiments with a stream of single photons, having a 98 micron temporal coherence length at an emission rate of 6,800 photons per second, finding the same results as described above. In the latter experiment there was an average separation of approximately 2 kilometers between photon wavepackets and, correspondingly, a vanishing probability of the overlap of two photon wavepackets in the experimental apparatus, demonstrating that the principles governing the interaction of light with polarizers are fundamentally quantum phenomena which apply to individual photon wavepackets.
In summary, it has been demonstrated that certain processes can produce correlated pairs of quantum objects, such as photons, which have entangled polarization states; observation of the polarization of one photon sets the polarization state of its companion to the compatible value required by the applicable Conservation of Angular Momentum constraint on that entangled photon pair. It has also been demonstrated that the linear polarization state of a photon can be altered by causing the photon to make a sequence of quantum choices as it passes through a series of linear polarizers oriented in a plurality of polarization bases. It has further been demonstrated that the passage of polarization-entangled photons through polarizing elements does not cause the loss of their polarization entanglement and that the persistence of entanglement in a polarization-entangled photon pair does not require that the photons always exist in a superposition of polarization states in all polarization bases.
In light of these teachings, the above objects of the present invention are accomplished by providing a method and apparatus for controlling the quantum state probability distribution of ONE quantum object of a pair of entangled quantum objects, which method includes the steps of providing a pair of entangled quantum objects having a prepared quantum state probability distribution, providing a means for controlling the quantum state probability distribution of the ONE quantum object by using said controlling means to alter the probability distribution of the observable quantum states of the OTHER quantum object of the pair of entangled quantum objects, choosing whether to use said controlling means to alter the probability distribution of the quantum states of the OTHER quantum object, choosing whether to observe the quantum state of the OTHER quantum object, and subsequently observing the quantum state of the ONE quantum object of said pair of entangled quantum objects to determine if said prepared quantum state probability distribution of said ONE quantum object has been altered by an observation of the quantum state of the OTHER quantum object. By such method, information may be selectively transmitted on observation of the quantum state probability distribution of the ONE quantum object by selectively controlling the quantum state probability distribution of the OTHER quantum object of the pair of entangled quantum objects and thereby selectively choosing whether to affect an alteration of the quantum state probability distribution of the ONE quantum object which is subsequently observed.
The method of the invention is suitable for a variety of quantum objects including fermions, atoms, and bosons, including, in particular, photons. The pair of entangled quantum objects may be provided as a part of a pair of streams of entangled quantum objects which may be provided by any one of a number of means including, but not limited to, a two-quantum absorption/two-quantum emission process, such as spin conserving two photon atomic emission processes including, for example, atomic cascade and spontaneous emission from atomic deuterium or atomic calcium, spin-conserving subatomic particle interactions, such as electron-positron annihilation radiation emission or low-energy proton-proton scattering, and optical parametric down conversion processes, including both Type I and Type II parametric down conversion.
The source of the pair of entangled quantum objects may provide a pair in the singlet state, a superposition of states, or in a definite state. When the pair of entangled quantum objects is provided in a definite quantum state, the quantum state probability distribution can be transformed into a superposition of states, if desired, by various means, such as by rotating the plane of polarization, or spin direction, of one stream of quantum objects and combining it with the other, unrotated stream of quantum objects. Ou and Mandel 1, supra. (Entangled photons emitted by certain non-linear parametric down-conversion crystals can be emitted in a definite polarization state in one basis, but which are completely indefinite in a complimentary basis, furthermore, omnidirectional polarization correlation effects can still be obtained by performing certain additional operations on the photons.)
The means for controlling the quantum state probability distribution of the ONE quantum object by using the means to choose the quantum state probability distribution of the OTHER quantum object consists of quantum spin selection or quantum spin altering devices such as polarizing beam splitters, Nichols prisms, tourmaline crystals, calcite crystals, electro-optic crystals, non-linear optical crystals, birefringent polarizing elements, wave plates, Kerr cells, Pockels cells, Faraday rotators, optically rotating materials and solutions, polarizing plastic sheet material (xe2x80x98Polaroidxe2x80x99 polarizers), polarization preserving optical fiber, Stem-Gerlach magnets, and similar optical polarization and spin selection components and combinations thereof. These quantum spin selection or quantum spin altering devices may be used in combination with detection devices or devices to absorb and observe the quantum spin state of the OTHER quantum object.
Preferably, the pair of entangled quantum objects is provided as a part of separated streams of entangled quantum objects. In the case of entangled photons, this may be accomplished by use of a device selected from the group consisting of lenses, prisms, mirrors, beam splitters, polarizing beam splitters and combinations thereof in conjunction with the source for providing such correlated photons. These devices may also be further employed to provide an equal probability of first detecting either photon of a pair in either stream, if desired. In the case of entangled quantum objects other than photons, these means may be accomplished by use of devices which are the functional equivalent of the optical devices, such as the use of a uniform magnetic field to act as a xe2x80x98prismxe2x80x99, or the use of a confined electric field to act as a xe2x80x98lensxe2x80x99 for charged entangled quantum objects, such as spin-entangled protons.
The step of choosing whether to alter and observe the probability distribution of the quantum states of the OTHER quantum object may selectively include either observing or not observing the quantum state of the OTHER quantum object in one of a plurality of polarization, or spin direction, bases, depending upon whether the user of the method desires to transmit information by modulating the quantum state probability distribution of the ONE quantum object, or not. In addition, by observing the quantum state of the OTHER quantum object by means of a spin selection device, it is possible to select whether to alter or not to alter the probability distribution of the ONE quantum object depending upon the choice of spin basis of the spin selection device.
In the case of polarization-entangled photons it is possible to select whether or not to alter the probability distribution of the ONE photon depending on the choice of polarization basis of the polarization selection device used to observe the polarization state probability distribution of the OTHER photon, and this choice may selectively include either observing or not observing the polarization state probability distribution of the OTHER photon.
My invention may be more completely understood by reference to the drawings and detailed description of the preferred embodiment provided below.